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Found the bum FAQ info:
Test 2. A further diagnostic test is to jumper the two larger wires leading into the radio suppression relay connector. If the fan starts, you've jumpered the wrong connector. If the engine then is able to start, your relay is defective. If not, your problem is elsewhere. Don't leave the jumper in place or your battery will discharge: this is for testing only.
• IMO,the FAQ is littered with sound good but un-vetted "tips" like this, which is not true at all, based on green book diagrams.
As to your current question:
"am still curious to know what the underlying problem is. why doesn't a known good relay work."
• I'm stumped for now, thinking only that something believed to be true is really false, e.g. the "known good" RS relay or substituted FI relay. Or it may be that the relay coil is not being energized. Something not yet tested.
The FI main relay powers the RSR coil. I would use a 12V test light to back-probe the RSR connector (BLUE-YELLOW wire) to see if coil voltage is there with Key ON, as it should be.
EDIT at 9:30PM EST... Actually you don't have to "back-probe" the relay plug. It would be easier and more direct just to disconnect the plug and probe the the Blue-Yellow wire's terminal pin. The voltage should be there with the key On.
I like a test light for something like this because it will fail to light or be noticeably dim if there is high resistance in the circuit, where a multimeter will boldly show a "ghost" of 12 volts.
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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